1. Field of the Invention
The invention relates to an inert gas fire-extinguishing system for reducing the risk of and extinguishing fires in a protected room, wherein the inert gas fire-extinguishing system includes at least one high-pressure gas tank in which an oxygen-displacing gas is stored under high pressure, wherein the high-pressure gas tank is connectable to a collecting line via a quick-opening valve; and wherein an extinguishing line is further provided which is connected on one side to the collecting line via a pressure-reducing device and on the other side to extinguishing nozzles.
2. Description of the Related Art
This type of inert gas fire-extinguishing system is known in principle in the prior art. For example, the DE 198 11 851 A1 German patent application describes an inert gas fire-extinguishing system designed to lower the oxygen content in an enclosed room (hereinafter referred to as “protected room”) to a specific base inerting level and, in the event of a fire, to quickly lower the oxygen content further to a specific full inerting level, thereby enabling the effective extinguishing of a fire which has broken out in the protected room, while at the same time keeping the space required for inert gas cylinders in which oxygen-displacing gas is stored under high pressure to a minimum.
The basic principle behind inert gas fire-extinguishing technology is based on the knowledge that in closed rooms which are only entered occasionally by humans or animals, and in which the equipment housed therein reacts sensitively to the effects of water, the risk of fire can be countered by reducing the oxygen concentration in the relevant area to a value of e.g., approximately 12% by volume on average. At such a (reduced) oxygen concentration, most combustible materials can no longer ignite.
The main areas of application for inert gas extinguishing technology accordingly include IT areas, electrical switching and distribution rooms, enclosed facilities as well as storage areas containing high-value commercial goods. The extinguishing effect resulting from this method is based on the principle of oxygen displacement. As is known, normal ambient air consists of 21% oxygen by volume, 78% nitrogen by volume and 1% by volume of other gases. For extinguishing purposes, the oxygen content of the atmosphere within the enclosed room is decreased by introducing an oxygen-displacing gas, for example nitrogen. An extinguishing effect is known to begin as soon as the percentage of oxygen drops below about 15% by volume. Depending upon the combustible materials stored in the protected room, it may be necessary to further lower the percentage of oxygen to the 12% by volume value as cited as an example above. The term “base inerting level” as used herein is to be understood as referring to a reduced oxygen content compared to the oxygen content of the normal ambient air, however, whereby this reduced oxygen content poses no danger of any kind to persons or animals such that they can still enter into the protected room without any problem (i.e., without any special protective measures such as oxygen masks, for example). The base inerting level corresponds to an oxygen content within the protected room of e.g., approximately 15%, 16% or 17% by volume. On the other hand, the term “full inerting level” is to be understood as referring to an oxygen content which has been further reduced compared to the oxygen content of the base inerting level such that the flammability of most materials has already been decreased to the extent that they are no longer able to ignite. Depending upon the fire load inside the respective protected room, the full inerting level generally ranges from 11% to 12% of oxygen concentration by volume.
In a multi-stage inerting method as known for example from the DE 198 11 851 A1 printed publication, in which the oxygen content is lowered in progressive stages, an “inert gas extinguishing technology” is thus, employed to first reduce the oxygen content in the protected room to a specific lowered level (base inerting level) of e.g., 16% by volume by flooding the room at risk of or already on fire with oxygen-displacing gas such as carbon dioxide, nitrogen, noble gases or mixtures thereof, whereby in the event of a fire or when otherwise needed, the oxygen content is then further reduced to a specific full inerting level of e.g., 12% by volume or lower. If an inert gas generator, for example a nitrogen generator, is used as an inert gas source in such a two-stage inerting method for reducing the oxygen content to the first lowered level (base inerting level), this can achieve being able to keep the number of high-pressure gas tanks as needed for full inertization, in which the oxygen-displacing gas or gas mixture (hereinafter also referred to simply as “inert gas”) is stored in compressed form, as low as possible.
In practical use of the above-described and known per se two-stage inerting method, however, the fact that the inerting of the protected room to set a predetermined lowered level, such as, for example, the base or full inerting level, cannot ensue according to a predefined sequence of events has proven problematic in certain cases. In particular, the currently known multi-stage inert gas fire-extinguishing systems do not allow for the fact that it might at times be desired to gradually render a protected room inert; i.e., regulating the predefined lowered to levels in progressive stages according to different sequences of events, wherein these sequences of events can be adapted to specific conditions.
In a multi-stage inerting method as known for example from the DE 198 11 851 A1 printed publication, when inert gas is introduced into the atmosphere of the protected room so as to set a specific lowered level, the method in particular does not differentiate between setting a base inerting level versus a full inerting level in the atmosphere of the room. In other words, regardless of which lowered level is to be set in the protected room with the known method, the inerting of the protected room follows one and the same inerting curve. To be understood by the term “inerting curve” as used herein is the temporal variation of the oxygen content when oxygen-displacing gas (inert gas) is introduced into the spatial atmosphere of the protected room. Due to this limitation, an inert gas fire-extinguishing system as described, for example, in the DE 198 11 851 A1 printed publication is not suited or only conditionally suited as a multi-zone fire-extinguishing system, since inertization cannot be adapted to individual protected rooms. Particularly not taken into account, is that in the case of differently dimensioned protected rooms, for example, the maximum volume of inert gas introduced per unit of time for inerting purposes should be adapted to the respective protected room. The given pressure relief as well as pressure resistance of the room's spatial shell in particular dictate the maximum allowable volume of inert gas introduced per unit of time in this context. This maximum allowable volume of inert gas introduced into the protected room per unit of time ultimately determines the sequence of events during the inerting of the protected room; i.e., the inerting curve applicable to the room.
When employing an inert gas fire-extinguishing system as a multi-zone system, thus, one in which one and the same inert gas fire-extinguishing system provides preventative fire control or extinguishing for a plurality of protected rooms, the problem thus, arises that regardless of which of the multiple protected rooms is to be flooded with oxygen-displacing gas, each protected room is rendered inert according to one and the same sequence of events. Hence, with conventional multi-zone fire-extinguishing systems, a protected room of relatively small spatial volume is fed the same volume of oxygen-displacing gas per unit of time as a protected room having a proportionally larger spatial volume. Since the volume of inert gas which can be supplied per unit of time by the inert gas fire-extinguishing system is particularly dependent on the given pressure-relieving measures for the respective protected room, this means that the inerting of a protected room may sometimes take considerably longer as would actually be possible.
Based on this problem as set forth, the invention is based on the task of further developing an inert gas fire-extinguishing system as known for example from the DE 198 11 851 A1 printed publication such that rendering a protected room inert; i.e., setting a lowered level in the spatial atmosphere of the protected room, can ensue pursuant different sequences of events.